This invention relates to a lubrication arrangement for an engine and more particularly to an arrangement for lubricating and supplying lubricant to certain components of the valve actuating mechanism for an engine.
The use of overhead valves operated by overhead mounted camshafts is well known. Although there are some advantages to direct valve actuation, the use of a rocker arm actuator has the advantage of permitting the incorporation of a hydraulic lash adjuster. Conventionally it has been the practice to supply lubricant to the lash adjusters for their operation and to the journals of the associated camshaft in a series flow relationship. Although this has the advantage of simplicity, it has certain disadvantages. Specifically, with a series flow arrangement when the engine is turned off, the fact that the camshaft journals are open to the atmosphere will cause leak down of the lubricant. That is, because the cam journals are generally open, the system does not maintain pressure and lubricant can drain down back through the series flow arrangement into the lubricant reservoir through the oil pump. This means that the lubricant in the lifters will become depleted when the engine is shut down. This can give rise to obvious difficulties on restarting.
It is, therefore, a principal object of this invention to provide an improved lubricating system for an engine and for supplying lubricant to hydraulic lash adjusters.
It is a further object of this invention to provide a lubricating system for an engine, including hydraulic lash adjusters wherein the leak down of the lash adjusters when the engine is shut off is substantially reduced.
As has been previously noted, the normal arrangement for an engine having a camshaft and hydraulic lash adjusters is to supply lubricant through a common conduit from the lubricant pump to the lash adjusters and the cam journals. Frequently the engine may employ two camshafts, each of which operates its own series of valves through an actuating mechanism that includes its own series of lash adjusters. With the type flow arrangement previously proposed, the pressure of the lubricant supplied to the lash adjusters will depend upon its distance from the lubricant pump and this means that the adjusters associated with one camshaft may receive lubricant at a substantially lower pressure than those associated with the other camshaft.
It is, therefore, a still further object of this invention to provide a lubricating system for an engine having a pair of camshafts and lash adjusters associated with each of them wherein the lash adjusters are all supplied with substantially the same pressure.
In an arrangement incorporating a system for precluding leak down of the hydraulic lifters, a still further problem can result, particularly where the arrangement utilizes two camshafts and a plurality of lifters associated with it. Frequently, the arrangement is such that each cylinder of the engine is provided with different numbers of intake and exhaust valves. Where this is the case, a greater number of hydraulic lash adjusters may be associated with one camshaft than the other. This further aggravates the problems already discussed.
It is, therefore, a further object of this invention to provide a lubricating system for an engine embodying two camshafts, each of which operates a different number of hydraulic lash adjusters and wherein all of the lash adjusters will be supplied with substantially the same pressure.
In connection with valve arrangements of the type already described, it is generally necessary to deliver oil to the camshafts through the cylinder block and cylinder head. The camshafts are conventionally journaled on the cylinder head by bearing surfaces formed integrally with the cylinder head and separate bearing caps that are affixed to the cylinder head. With such an arrangement, it is generally the practice to deliver the oil to one end of the camshaft by means of a passage that is formed in the cylinder head and this obviously adds to the length of the engine. Also, the internal passages of the cylinder head may, itself, present certain problems in connection with maintaining a compact construction.
It is, therefore, a still further object of this invention to provide an improved arrangement for delivering lubricant to the camshafts of an overhead cam internal combustion engine, wherein certain of the delivery passages are formed externally of the cylinder head.